JPH07245870A - Lightning surge protective circuit - Google Patents

Abstract

PURPOSE:To surely protect a subscriber's circuit from the overvoltage of a steep negative surge voltage generated in a subscriber's line by providing a capacitor, a diode and a charging circuit for compensating for the delay of operation of a surge arrester. CONSTITUTION:A charging circuit 38 charges a capacitor 36 up to such a voltage that a diode 35 does not make continuity at the time of usual operation. For that reason, since an inverse bias voltage is applied to the diode 35, so that the cathode terminal comes into a high-impedance state, the capacitor 36 is cut off from a subscriber's line 31, so that the existence of the capacitor 36 does not have influence upon a call. While a negative surge voltage is generated in the subscriber's line 31 and the voltage exceeds the charging voltage of the capacitor 36 and the surge arrester 34 actually operates, the diode 35 comes into the continuity state and a current is supplied from the capacitor 36 to the subscriber's line 31 and a voltage drop is generated in a resistor 33, so that a large negative voltage is not applied to the input of a feeding part 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightning surge protection circuit for protecting a subscriber circuit from a lightning surge voltage generated on a subscriber line of an exchange. In recent years, there has been a demand for a lightning surge protection circuit having a protection capability that can sufficiently cope with a surge having a steep waveform.

[0002]

2. Description of the Related Art As shown in the conventional example of FIG. 7, in a conventional subscriber circuit, a BSH circuit 61 (feeding section) enters and exits 2
For each of the subscriber lines 62 and 63 of the book, a resistor 64,
A lightning surge protection circuit including 66 and 65, 67, surge arresters 68 and 69, and diodes 70 and 71 is installed.

This lightning surge protection circuit grounds the surge current through the diodes 70 and 71 when a positive surge voltage is generated on the subscriber line, and turns on the surge arresters 68 and 69 when a negative surge voltage is generated. The BSH circuit 61 is protected by grounding the surge current via the via.

[0004]

However, when a negative surge voltage having a steep rising waveform that reaches a very large voltage in a short time is generated on the subscriber line, the surge voltage reaches the operating voltage of the arrester. In some cases, a fatal excessive voltage may be applied to the BSH circuit within a short delay time from when the arrester actually operates. FIG. 3 shows the situation. The voltage indicated by the broken line in the figure is actually applied to the BSH circuit.

The present invention has been made in view of the above problems, and a lightning surge protection circuit capable of reliably protecting a subscriber circuit from an excessive voltage even against a steep negative surge voltage generated in a subscriber line. The purpose is to provide.

[0006]

FIG. 1 is a diagram (1) for explaining the principle of the present invention. The lightning surge protection circuit of the present invention is provided in the subscriber circuit of the exchange, and is a surge that has been conventionally installed to ground the lightning surge entering from the subscriber line 31 connected to the subscriber circuit. In addition to the arrester 34, a capacitor 36 for compensating the operation delay of the surge arrester 34, a diode 35, and a charging circuit 38 are provided. The diode 35 is connected between the capacitor 36 and the subscriber line 31 with the direction of the subscriber line 31 in the forward direction, and the other terminal of the capacitor 36 is grounded. The charging circuit 38 is configured to charge the capacitor 36 to a voltage at which the diode 35 does not conduct during normal operation.

In FIG. 1A, the charging circuit 38 is composed of a resistor 37 having a high resistance value and a DC power supply V _BB, and the power supply V _{BB is used.}
Through a resistor 37 to a diode 35 and a capacitor 36
It is connected to the connection point with.

[0008] In FIG. 1 (b), constitute a charging circuit 38 by the resistor 39 of low resistance value and a DC power supply V _BB, the power supply V _BB
Through a resistor 39 to a diode 35 and a capacitor 36
In addition to being connected to the connection point with, the power line 40 in the subscriber circuit is also connected.

FIG. 2 is a diagram (2) for explaining the principle of the present invention. FIG. 2A shows a circuit configuration for sharing the surge arrester 47 with the two subscriber lines 41 and 42 forming the communication path. One terminal of the surge arrester 47 is connected to each of the two subscriber lines via diodes 45 and 46 whose forward direction is the subscriber line direction, and the other terminal is grounded.

FIG. 2B shows a circuit configuration for sharing the capacitor 50 between the two subscriber lines 41 and 42 forming a communication path. One terminal of the capacitor 50 is connected to each of the two subscriber lines via diodes 48 and 49 whose forward direction is the subscriber line direction, and the other terminal is grounded.

[0011]

The capacitor 36 of FIG. 1 is charged so that it does not become higher than the voltage of the subscriber line 31 during normal operation. Therefore, the reverse bias voltage is applied to the diode 35 and the cathode terminal is in a high impedance state, so that the capacitor 35 is disconnected from the subscriber line 31, and the presence of the capacitor 35 does not affect the call.

From the time when the negative surge voltage is generated on the subscriber line 31 and the voltage exceeds the charging voltage of the capacitor 36 until the surge arrester 34 actually operates, the diode 3
5 becomes conductive and from the capacitor 36 to the subscriber line 31
The current is supplied to the resistor 33 and a voltage drop occurs in the resistor 33, thereby preventing an excessive negative voltage from being applied to the input part of the power feeding part 32.

Resistor 3 constituting the charging circuit of FIG. 1 (a)
7 has a high resistance value in order to prevent an excessive current from flowing at the time of charging or entering a negative surge to destroy the power supply and the circuit connected to the power supply.

As in the charging circuit shown in FIG. 1B, if the DC power supply is commonly connected to the capacitor 36 and the power feeding section 32 via the resistor 39 having a low resistance value, the capacitor 3
6 can also be used for noise reduction of the power supply voltage during normal operation.

If the surge arrester 47 is connected so as to be shared by the subscriber lines 41 and 42 as shown in FIG. 2 (a), the surge arrester is activated when a negative surge voltage occurs on one or both of these subscriber lines. When 47 is turned on and a surge current is supplied from the ground to the subscriber line 41 (or 42) through the diode 45 (or 46) and a voltage drop occurs in the resistor 43 (or 44), an excessive current is supplied to the power supply unit side. Prevents negative voltage from being applied.

If the capacitor 50 is connected so as to be shared by the subscriber lines 41 and 42 as shown in FIG. 2B, when a negative surge voltage occurs on one or both of these subscriber lines, the surge voltage From the capacitor 50 to the diode 48 (or 49) after the voltage exceeds the charging voltage of the capacitor 50 until the surge arrester 47 actually operates.
An electric current is supplied to the subscriber line 41 (or 42) through the resistor 43 (or 44) to cause a voltage drop, thereby preventing an excessive negative voltage from being applied to the power supply unit side.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows an embodiment of the present invention. The two subscriber lines (chip line 2 and ring line 3) from the subscriber terminal are connected to the corresponding subscriber circuit in the exchange, and are connected to the BSH circuit 1 (power supply unit) in the subscriber circuit. . The lightning surge protection circuit is installed at the entrance of the BSH circuit 1.

This lightning surge protection circuit is divided into a first stage and a second stage. In the first stage, 47Ω surge protection resistors 4 and 5 inserted in the chip line 2 and the ring line 3, respectively, and then a diode bridge (diode 9 to diode 9-) arranged between the chip line 2 and the ring line 3. 12) and a surge arrester 8 connected to the diode bridge. One terminal of the surge arrester 8 is a diode 9
And 10 anode terminals, and the other terminal is grounded. The cathode terminals of the diodes 9 and 10 are connected to the tip line 2 and the ring line 3, respectively. The anode terminals of the diodes 11 and 12 are the tip line 2 and the ring line 3 respectively.
And the cathode terminal is grounded.

In the second stage, 10Ω surge protection resistors 6 and 7 inserted in the tip line 2 and the ring line 3, respectively, and then a diode bridge () arranged between the tip line 2 and the ring line 3 ( It is composed of a diode 15-18), a 0.47 μF capacitor 14 connected to the diode bridge, and a charging circuit (100 kΩ resistor 13 and DC power supply V _BB ). The capacitor 14 has one terminal connected to the anode terminals of the diodes 15 and 16,
The other terminal is grounded. The cathode terminals of the diodes 15 and 16 are connected to the tip line 2 and the ring line 3, respectively. The anode terminals of the diodes 17 and 18 are connected to the tip line 2 and the ring line 3, respectively, and the cathode terminals are grounded.

The charging circuit supplies the charging current to the capacitor 14 from the DC power supply for the BSH circuit 1 through the resistor of 100 kΩ, so that the diode 1
The voltage at the connection point between the capacitors 5 and 16 and the capacitor 14 is V _BB (
48V). Since both the tip line 2 and the ring line 3 have voltages in the range of 0 to V _BB , the diodes 15 and 16 are applied with voltages in opposite directions. Therefore, during normal operation, the cathode terminals of these diodes are in a high impedance state and disconnect the capacitor 14 from the chip line 2 and the ring line 3, so that the presence of the capacitor 14 does not affect the call.

The diodes 11 and 12 in the diode bridge of the first stage and the diodes 17 and 18 in the diode bridge of the second stage are added to correspond to the positive surge voltage generated in the subscriber line.

For example, when a lightning surge enters the chip line 2 and a positive surge voltage is generated, a surge current is grounded from the chip line 2 through the diode 11 to cause a voltage drop in the resistor 4 and an excessive voltage in the subsequent stage. Prevents voltage from being applied. Further, the surge current flowing into the second stage is ground-faulted through the diode 17 to cause a voltage drop in the resistor 6 to ensure the voltage clamp capability.

The same action as described above also works for the positive surge voltage generated in the ring line 3 and the application of an excessive positive voltage to the BSH circuit 1 is prevented. Further, even if a positive surge voltage is generated on both subscriber lines at the same time, it can be dealt with in the same manner.

When a negative surge voltage occurs on the subscriber line,
The surge arrester 8 in the first stage conducts and the surge current is absorbed by flowing the surge current to the ground. However, when a negative surge voltage with a steep rising waveform occurs, the current from the capacitor 14 in the second stage to the subscriber line is increased. Is supplied to compensate the operation delay of the surge arrester 8.

For example, when a lightning surge enters the chip line 2 and a steep negative surge voltage is generated, the surge arrester 8 actually operates after the surge voltage exceeds the operating voltage of the surge arrester 8. The voltage of the chip line 2 becomes lower than the voltage at the connection point between the second stage diode 15 and the capacitor 14, and the diode 15 becomes conductive, so that the capacitor 1
The discharge current from 4 is supplied to the chip line 2 and a voltage drop occurs in the resistors 4 and 6. This suppresses an increase in the negative voltage of the chip line 2 and prevents an excessive negative voltage from being applied to the BSH circuit 1 within the operation delay time of the surge arrester 8.

The same action as described above also works for the negative surge voltage generated in the ring line 3, and the application of an excessive negative voltage to the BSH circuit 1 is prevented. Further, even if a negative surge voltage is simultaneously generated on both subscriber lines, it is possible to deal with it in the same manner.

The surge arrester 8 is a diode 9,
Since it is connected to the chip line 2 and the ring line 3 via 10, the surge absorption capacity is reduced by the voltage generated in the diode when a surge current flows, but the current supplied by the second-stage capacitor 14 Is compensated for by.

In the embodiment shown in FIG. 4, a resistor 13 having a high resistance value (100 kΩ) is used to charge the capacitor 14.
This is to prevent the power supply and other circuits connected to the power supply from being destroyed as a result of an excessive current flowing from the power supply during charging.

The other embodiment shown in FIG. 5 differs from the embodiment shown in FIG. 4 in the configuration of the charging circuit. In this case, the power supply voltage V _BB is connected to both the capacitor 14 and the BSH circuit 1 via the resistor 19 having a low resistance value (1Ω). With this configuration, the capacitor 14 can also be used for noise reduction of the power supply voltage during normal operation. Since the charging line of the capacitor 14 is shared with the power supply line of the BSH circuit 1, the resistance value of the resistor 19 cannot be increased, but the capacitance of the capacitor 14 is sufficiently increased and the capacitor 14 is in the second stage. If the resistor 14 is placed in the immediate vicinity of the diode bridge to reduce the impedance of the line, the capacitor 14 functions as a smoothing capacitor, so there is no problem even if the resistor 19 is inserted on the power supply voltage V _BB side. If the resistor 19 is a fuse resistor for safety, even if an excessive current flows, the fuse is blown and the operation of this subscriber circuit is stopped, but the power supply and other circuits connected to the power supply are stopped. Will not be damaged.

The embodiment of FIG. 6 shows a case where lightning surge protection circuits are separately provided for two subscriber lines. this is,
This is a circuit in which a circuit portion corresponding to a steep negative surge is added to the conventional lightning surge protection circuit shown in FIG. That is, a circuit portion including a diode 74, a capacitor 76, and a resistor 72 is added to the subscriber line 62, and a circuit portion including a diode 75, a capacitor 77, and a resistor 73 is added to the subscriber line 63. DC power supply V
By connecting to _BB and ground, a function of protecting the BSH circuit 61 from a steep negative surge is added. In this embodiment, a surge arrester 68 and a capacitor 76 are separately installed for the subscriber line 62, and a surge arrester 69 and a capacitor 77 are separately installed for the subscriber line 63, and the diode for absorbing the positive surge is one. Since it is installed only at the stage (diodes 70 and 71), no diode bridge is formed.

[0031]

As described above, according to the present invention, the subscriber circuit can be reliably protected even when a sharp lightning surge that causes a problem in the operation delay time of the surge arrester enters the subscriber line. You can According to the experiment, ± 2.5 kV,
It has been confirmed that it can also cope with lightning surges having a waveform of 2/10 μs (US).

Further, according to the third aspect of the invention, the surge protection capacitor can also be used for noise reduction during normal operation, which contributes to the improvement of circuit reliability.

Further, according to the inventions of claims 4 and 5, since the expensive surge arrester and each one large-capacity capacitor can be shared by two subscriber lines, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a principle explanatory view (1) according to the present invention.

FIG. 2 is a principle explanatory view (2) according to the present invention.

FIG. 3 is a diagram illustrating an operation delay of a surge arrester when a negative surge voltage having a steep waveform is generated.

FIG. 4 is a diagram showing an example of the present invention.

FIG. 5 is a diagram showing another embodiment of the present invention.

FIG. 6 is a diagram showing still another embodiment of the present invention.

FIG. 7 is a diagram showing a conventional example.

[Explanation of symbols]

 1 BSH Circuit 2 Chip Line 3 Ring Line 4-7 Surge Protection Resistor 8 Surge Arrestor 9-12, 15-18 Diode 13 Resistor (High Resistance Value) 14 Capacitor 19 Resistor (Low Resistance Value) 31 Subscriber Line 32 Power Supply Section 33 Surge Protection Resistor 34 Surge Arrestor 35 Diode 36 Capacitor 37 Resistor (High Resistance Value) 38 Charging Circuit 39 Resistor (Low Resistance Value) 41, 42 Subscriber Line 43, 44 Surge Protection Resistor 45 , 46, 48, 49 Diode 50 Capacitor 51 Resistor 61 BSH circuit 62, 63 Subscriber line 64-67 Resistor for surge protection 68, 69 Surge arrester 70, 71, 74, 75 Diode 72, 73 Resistor 76, 77 Capacitor

Claims (5)

[Claims] 1. A lightning surge protection circuit provided in a subscriber circuit of a switchboard, comprising a surge arrester (34) for grounding a lightning surge entering a subscriber line (31), and a capacitor (36), A diode (35) connected between the capacitor and the subscriber line with the subscriber line in the forward direction, and a charging circuit (38) for charging the capacitor to a voltage such that the diode does not conduct during normal operation. Lightning surge protection circuit characterized by having and. 2. The lightning surge protection circuit according to claim 1, wherein the charging circuit is a circuit for supplying a charging current to the capacitor from a DC power supply (V _BB ) through a high resistance resistor (37). 3. The charging circuit is a circuit for supplying a current from a direct current power supply (V _BB ) to the capacitor and a power supply line (40) in a subscriber circuit through a low resistance resistor (39). The lightning surge protection circuit according to claim 1. 4. The surge arrester forming a communication path 2
One surge arrester (47) is shared by one subscriber line (41, 42) and one terminal of the surge arrester is a diode (45, 4) whose forward direction is the subscriber line direction.
The lightning surge protection circuit according to any one of claims 1 to 3, wherein the lightning surge protection circuit is configured to be connected to each of the two subscriber lines according to 6) and have the other terminal grounded. 5. One capacitor (5) for the two subscriber lines (41, 42) forming a communication path.
0), one terminal of the capacitor is connected to each of the two subscriber lines by a diode (48, 49) whose forward direction is the subscriber line direction, and the other terminal is grounded. The lightning surge protection circuit according to any one of claims 1 to 4, which is configured.